Fixing Unit

The present invention relates to a fixing unit that heats a sheet on which an image is formed by ejecting ink to fix the image onto the sheet.

Japanese Patent Application Laid-Open Publication No. 2018-136392 describes a configuration in which a temperature of a heater is measured using a sensor disposed on the heater that heats a belt, and energization control with respect to the heater is changed when an abnormal temperature rise is detected.

According to a first aspect of the present invention, a fixing unit includes an endless belt configured to heat a sheet on which an ink image is formed to fix the image onto the sheet, a heater disposed inside the belt in such a manner as not to be in contact with the belt and configured to heat the belt by emitting an electromagnetic wave, a reflecting member configured to reflect the electromagnetic wave emitted by the heater toward a region of the belt, with the heater being disposed inside the reflecting member, a temperature detection unit disposed outside the reflecting member and configured to detect a temperature of the region, a fan configured to generate an airflow, and, a flow path forming portion provided inside the belt and forming a flow path through which the airflow generated from the fan flows. The temperature detection unit is disposed inside the flow path forming portion.

According to a second aspect of the present invention, a fixing unit includes an endless belt configured to heat a sheet on which an ink image is formed to fix the image onto the sheet, a first heater and a second heater disposed inside the belt in such a manner as not to be in contact with the belt and configured to heat the belt by emitting electromagnetic waves, a first reflecting member configured to reflect the electromagnetic wave emitted by the first heater toward a first region of the belt, with the first heater being disposed inside the first reflecting member, a second reflecting member configured to reflect the electromagnetic wave emitted by the second heater toward a second region of the belt, with the second heater being disposed inside the second reflecting member, a temperature detection unit disposed outside the first reflecting member and the second reflecting member, and configured to detect a temperature one of the first region and the second region, and, a fan configured to generate an airflow. The airflow generated from the fan flows in a width direction of the belt intersecting a rotation direction of the belt along a part of the first reflecting member and a part of the second reflecting member. The temperature detection unit is disposed in a flow path through which the airflow generated from the fan flows.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

A first embodiment will be described with reference to. First, a schematic configuration of an inkjet recording apparatus of the present embodiment will be described with reference to.

The inkjet recording apparatusserving as an image forming system of the present embodiment uses an inkjet recording system that ejects ink to form an image on a sheet, and is a so-called sheet-type inkjet recording apparatus that forms an ink image on a sheet using two liquids of a reaction liquid and ink. The sheet may be, for example, a recording material capable of receiving ink, such as paper such as plain paper or thick paper, a plastic film such as a sheet for an overhead projector, a sheet having a special shape such as an envelope or index paper, and cloth.

As illustrated in, the inkjet recording apparatusof the present embodiment includes a feeding module, a print module, a drying module, a fixing module, a cooling module, a reverse module, and a stacking module. When the sheet S supplied from the feeding moduleis conveyed along a conveyance path in each module, various processing is performed, and the sheet S is finally discharged to the stacking module.

Note that the feeding module, the print module, the drying module, the fixing module, the cooling module, the reverse module, and the stacking modulemay have separate casings, and these casings may be connected to configure the inkjet recording apparatus. Alternatively, the feeding module, the print module, the drying module, the fixing module, the cooling module, the reverse module, and the stacking modulemay be disposed in one casing.

The feeding moduleincludes storage compartments,, andthat store the sheet S, and the storage compartmentstoare provided to be drawable toward the front side of the apparatus in order to store the sheet S. The sheets S are fed one by one by a separation belt and a conveying roller in each of the storage compartmentsto, and conveyed to the print module. The number of storage compartmentstois not limited to 3, and may be 1, 2, or 4 or more.

The print moduleserving as an image forming unit includes a pre-image formation registration correction unit (not illustrated), a print belt unit, and a recording unit. The sheet S conveyed from the feeding moduleis corrected an inclination and a position of the sheet S by the pre-image formation registration correction unit and conveyed to the print belt unit. The recording unitis disposed at a position facing the print belt unitacross the conveyance path. The recording unitis an inkjet recording unit that forms an image by ejecting ink onto the sheet S by a recording head from above with respect to the conveyed sheet S. A plurality of recording heads that eject ink is arranged along a conveyance direction. In the present embodiment, in addition to four colors of yellow (Y), magenta (M), cyan (C), and black (Bk), a total of five line type recording heads corresponding to the reaction liquid are provided. The sheet S is sucked and conveyed by the print belt unitto secure a clearance with the recording head.

Note that the number of colors of ink and the number of recording heads are not limited to the above-described five. As the inkjet method, a method using a heat generating element, a method using a piezoelectric element, a method using an electrostatic element, a method using a micro electro mechanical systems (MEMS) element, and the like can be adopted. The ink of each color is supplied from each ink tank (not illustrated) to each recording head via each ink tube. The ink contains “0.1 mass % to 20.0 mass %” of a resin component, water, a water-soluble organic solvent, a coloring material, wax, an additive, and the like on the basis of the total mass of the ink.

When the sheet S on which an image is formed by the recording unitis conveyed by the print belt unit, deviation and color density of the image formed on the sheet S are detected by an in-line scanner (not illustrated) arranged downstream of the recording unitin the conveyance direction of the sheet S. Based on the deviation and the color density of the image detected by the in-line scanner, deviation of an image, density of an image, and the like to be formed on the sheet S are corrected.

The drying moduleserving as a drying apparatus includes a decoupling unit, a drying belt unit, and a warm air blowing unit. The drying modulereduces the liquid content of the ink and the reaction liquid applied to the sheet S in order to enhance the fixability of the ink to the sheet S by the subsequent fixing module. The sheet S on which the image is formed is conveyed to the decoupling unitdisposed in the drying module. In the decoupling unit, a frictional force is generated between the sheet S and the belt by the wind pressure of the wind blown from above, and the sheet S is conveyed by the belt. In this way, by conveying the sheet S placed on the belt by frictional force, deviation of the sheet S when the sheet S is conveyed over the print belt unitand the decoupling unitis prevented. The sheet S conveyed from the decoupling unitis sucked and conveyed by the drying belt unit, and the hot air is blown from the warm air blowing unitdisposed above the belt to dry the ink and the reaction liquid applied to the sheet S.

In this way, by heating the ink and the reaction liquid applied to the sheet S by the drying moduleand accelerating evaporation of moisture, it is possible to suppress an occurrence of so-called cockling in which the ink is scattered on the sheet S and a border-like line is formed around the sheet S. As the drying module, any device may be used as long as it is capable of drying the ink in a heating manner. For example, a hot air dryer or a heater is preferable. As an example of the heater, an electric wire heater or an infrared heater is preferable from the viewpoint of heating safety and heating energy efficiency. The drying method may be a combination of a method of applying hot air and a method of irradiating the surface of the sheet S with an electromagnetic wave (ultraviolet ray, infrared ray, or the like) or a conductive heat transfer method using contact with a heating element.

The fixing moduleserving as a fixing system includes a fixing belt unitserving as a fixing unit. The fixing belt unitcauses the sheet S conveyed from the drying moduleto pass between a heated upper belt unit and lower belt unit to fix the ink to the sheet S. The fixing belt unitwill be described in detail below.

The cooling moduleincludes a plurality of cooling units, and cools the high-temperature sheet S conveyed from the fixing moduleby the cooling units. For example, each of the cooling unitstakes outside air into a cooling box by a fan to increase the pressure in the cooling box, and blows air blown from the cooling box through the nozzle by the pressure against the sheet S to cool the sheet S. The cooling unitsare disposed on each of both sides of the conveyance path of the sheet S and cools both surfaces of the sheet S.

A conveyance path switching unitis provided in the cooling module. The conveyance path switching unitswitches the conveyance path of the sheet S according to the case of conveying the sheet S to the reverse moduleand the case of conveying the sheet S to a duplex conveyance path for duplex printing for forming an image on both surfaces of the sheet S.

The reverse moduleincludes a reverse portion. The reverse portionreverses the front and back sides of the conveyed sheet S and changes the front and back sides of the sheet S when the sheet S is discharged to the stacking module. The stacking moduleincludes a top trayand a stacking portion, and stacks the sheet S conveyed from the reverse module.

During duplex printing, the sheet S is conveyed to a conveyance path below the cooling moduleby the conveyance path switching unit. Thereafter, the sheet S is returned to the print modulethrough the duplex conveyance path of the fixing module, the drying module, the print module, and the feeding module. A reverse portionthat reverses the front and back of the sheet S is provided in a duplex conveying portion of the fixing module. The sheet S returned to the print modulehas an image formed by ink on the other surface on which no image is formed, and is discharged to the stacking modulethrough the drying module, the fixing module, the cooling module, and the reverse module.

Next, the fixing modulewill be described in detail with reference to.is a schematic view illustrating the fixing module. The fixing belt unitserving as a fixing unit is provided at the upper portion of the fixing module. The fixing belt unithas a substantially linear sheet conveyance pathfor receiving the sheet S discharged from the drying module, fixing the sheet S, and then delivering the sheet S to the cooling module(see). In each drawing, a front side of the inkjet recording apparatusis referred to as a front direction F, a back side thereof is referred to as a rear direction B, a right side thereof as viewed from the front is referred to as a rightward direction R, a left side thereof as viewed from the right is referred to as a left direction L, an upper side thereof is referred to as an up direction U, and a lower side thereof is referred to as a down direction D. An operation unit (not illustrated) operated by an operator is provided on the front side of the inkjet recording apparatus.

The fixing belt unitincludes an upper belt unitand a lower belt unit. The upper belt unitis disposed above the lower belt unitin the vertical direction. The upper belt unitincludes an upper belt, which is an example of a belt or a first belt, and a tension roller(stretching member or first stretching member) that applies tension to the upper belt. That is, the upper belt unitis an example of a belt unit (first belt unit), and detachably includes an upper beltthat conveys the sheet S. The lower belt unitis an example of a second belt unit, and includes a lower beltthat is an example of a nip portion forming member or a second belt, a tension roller(second stretching member) that applies tension to the lower belt, and a padhaving an arc-shaped curved surface. The padis disposed to form a nip with the upper beltvia the lower belt.

The sheet S is conveyed while being nipped by the nip between the upper belt unitand the lower belt unit. That is, as will be described below, the lower beltis disposed to face the upper belt unitwhen an upper door unitis located at a closed position and the upper belt unitis located at an upper storage position. At this time, the lower beltnips and conveys the sheet S together with the upper belt. The pressure of the nip is determined by the tension and thickness of the upper beltand the curvature of the pad. When the pressure of the nip is too high, there is a possibility that a phenomenon occurs in which the ink on the sheet S adheres to the upper belt unitand the ink is peeled off from the sheet S. Therefore, the pressure is preferably 1 Pa to 2000 Pa, and more preferably 1 Pa to 200 Pa.

When the curvature of the padis large, the conveyance path difference between the front and back surfaces of the sheet S is large, and there is a possibility that the sheet S and the belt rub against each other. When the curvature of the padis large, there is a possibility that a phenomenon occurs in which the sheet S itself memorizes the curved shape and curls. Therefore, the curvature radius of the padis desirably 50 mm or more. In addition, the curvature of the paddesirably has a curvature radius of 100,000 mm or less from the viewpoint of manufacturing accuracy. Due to these restrictions, in the present embodiment, the tension of the upper beltis set to 200 N, the thickness of the upper beltis set to 0.3 mm, the curvature of the padis set to 30,000 mm, and the pressure of the nip is set to about 16 Pa.

By adopting such a configuration, even a wide nip can be uniformly pressurized. As a result, even in a state where the temperature of the upper belt unitis a temperature corresponding to the melting point of wax or the boiling point of water, heat can be sufficiently transferred to the sheet S by increasing the contact time between the sheet S and the upper belt unit. However, if the nip is continuously formed after the heat is sufficiently transferred, a phenomenon occurs in which the ink adheres to the upper beltand the ink is peeled off from the sheet S, or a phenomenon occurs in which the upper beltand the sheet S rub against each other and the image is disturbed. Therefore, an excessively long contact time is not preferable. Therefore, the time taken for the leading end of the sheet S to emerge from an outlet of the nip after entering an inlet of the nip is desirably 0.5 s to 4 s. In the present embodiment, the sheet S is conveyed at 700 mm/s using the padhaving a length of 900 mm in the sheet conveyance direction, with the time required for the leading end of the sheet S to emerge from the outlet of the nip after entering the inlet of the nip being about 1.3 s. Note that since moisture is necessary when the ink penetrates into the sheet S, the upper beltand the lower beltare preferably impermeable to moisture so that moisture evaporated from the surface of the sheet S when the sheet becomes too hot does not escape through the upper beltor lower beltthat the surface of the sheet S contacts. In the present embodiment, for the upper beltand the lower belt, a belt material having a thickness of about 0.4 mm obtained by applying a polytetrafluoroethylene (PTFE) coating to a surface of a glass fiber base material is used in consideration of heat resistance, slidability, sealability, and durability.

As described above, the fixing belt unitserving as a fixing unit includes the upper belt unitand the lower belt unit, and the upper beltof the upper belt unitand the lower beltof the lower belt unitare brought into pressure contact with each other to form a nip portion N. The sheet Sis conveyed while being nipped by the nip portion N, and an image formed by the ink is fixed onto the sheet Sby applying pressure and heat at that time.

The upper belt unitincludes an endless upper beltserving as a belt or a first belt, a plurality of stretching rollers serving as a plurality of first stretching members that stretch the upper belt, and a first heating unit. The plurality of stretching rollers are an inlet roller, an outlet roller, a driving roller, a tension roller, a guide roller, a guide roller, and a steering roller. These rollers are arranged in order from the upstream side of the nip portion N in the rotation direction of the upper belt, and a rotation locus of the upper beltis thereby formed.

In addition, the nip portion N exists between the inlet rollerand the outlet roller. That is, the inlet rollerand the outlet rollerare disposed to sandwich the nip portion N therebetween in the rotation direction of the upper belt. In addition, the upper beltis stretched by the inlet rollerand the outlet rollerto form a first stretched surface. Each roller is supported by an upper frameserving as a first frame, which is a casing of the upper belt unit.

The lower belt unitincludes an endless lower beltserving as a belt or a second belt, a plurality of stretching rollers serving as a plurality of second stretching members that stretch the lower belt, and a second heating unit. The plurality of stretching rollers are a nip upstream guide roller, a nip upstream roller, a nip downstream roller, a driving roller, a tension roller, a guide roller, a guide roller, and a steering roller. These rollers are arranged in order from the upstream side of the nip portion N in the rotation direction of the lower belt.

In addition, the nip portion N exists between the nip upstream rollerand the nip downstream roller, and the padis disposed in the nip portion N. That is, the nip upstream rollerand the nip downstream rollerare disposed to sandwich the nip portion N therebetween in the rotation direction of the lower belt. The padserving as a supporting member abuts on an inner peripheral surface of the lower beltin the region of the nip portion N to support the lower belt. In other words, the nip upstream rollerand the nip downstream rollerare disposed on both sides of the padin the rotation direction of the lower belt. In addition, the lower beltis stretched by the nip upstream rollerand the nip downstream rollerto form a second stretched surface. The nip portion N is formed between the first stretched surfaceof the upper beltand the second stretched surface. A rotation locus of the lower beltis formed by the rollers and the pad. The rollers and the padare supported by a lower frameserving as a second frame, which is a casing of the lower belt unit.

The upper beltand the lower beltare driven to rotate by the frictional force between the surface of the rollerand the inner surface of the beltand the surface of the rollerand the inner surface of the beltwhen the driving rollersandof the respective belt units are rotated by respective motors (not illustrated). Rotation detection sensorsandare disposed on rotation shafts of the guide rollers (driven rollers)andthat are driven to rotate by rotation of the upper beltand the lower belt. The rotation detection sensorsandare elements constituted by magnets whose magnetic force is changed in the rotation direction of the guide rollersand, and detect the rotation of the upper beltand the lower beltby detecting changes in N and S poles caused by the rotation by a Hall sensor (not illustrated). In the present embodiment, the rotation detection sensor is an element constituted by a magnet, but a transmissive sensor that detects changes in light shielding and light transmission using a physical flag having an edge in the rotation direction of the driven roller may be used.

Next, the first heating unitand the second heating unitof the respective belt units will be described. The first heating unitis disposed inside the upper belt, and includes heating portions,, and. The heating portions include heaters,,,,, and, and reflectors (reflecting plates),, andserving as reflecting members, respectively (see). The first heating unitis attachable to and detachable from a first belt unit bodyincluding the upper belt.

The heaters,,,,, andincluded in heating portions,, and,,are disposed along a width direction of the upper beltthat intersects the rotation direction of the upper beltnot to be in contact with the upper beltto heat the upper beltby radiating heat. The reflectors,, andare disposed along the width direction, and reflect electromagnetic waves (radiant heat) emitted from the heaters,,,,, andtoward certain regions of the upper belt.

In the present embodiment, the first heating unitof the upper belt unitis disposed inside the upper beltand above the nip portion N to heat the upper beltfrom the inside. The first heating unitincludes a plurality of heating portions,, and. In the present embodiment, the three heating portions,, andare arranged side by side in the rotation direction of the upper belt.

The reflectors,, andare disposed to cover the peripheries of the heaters,,,,, andexcept for the side facing the upper belt. That is, the reflectors,, andare formed such that the heaters,,,,, andare open toward the nip portion N and both ends of the heaters,,,,, andin the width direction are covered. As a result, the reflectors,, andefficiently radiate the radiant heat of the heaters,,,,, andtoward the nip portion N.

That is, in the upper belt unit, the certain regions are regions of the inner peripheral surface of the upper beltwithin the range of the nip portion N, and the nip portion Nis directly heated by the plurality of heating portions,, and. As a result, heat can be efficiently transferred to the sheet S passing through the nip portion N. In the present embodiment, the regions within the range of the nip portion N heated by the plurality of heating portions,, andare regions of the inner peripheral surface (lower surface portion) of the upper belt, and are regions located upstream of the central position of the nip portion N in the direction of the sheet S passing through the nip portion Nis conveyed. In addition, the heating portions,, andperform temperature adjustment control such that the temperature of the upper beltis maintained at a predetermined temperature, by controlling the input power based on a value detected by a temperature sensorthat detects the surface temperature of the upper belt.

The second heating unitis disposed inside the lower belt, and includes heating portionsand. The heating portions include heaters,,, and, and reflectors (reflecting plates)andserving as reflecting members, respectively (see). The second heating unitis attachable to and detachable from a second belt unit bodyincluding the lower belt.

The heaters,,, andincluded in the heating portionsandare disposed along a width direction of the lower beltthat intersects the rotation direction of the lower beltnot to be in contact with the lower beltto heat the lower beltby radiating heat. The reflectorsandare disposed along the width direction, and reflect electromagnetic waves (radiant heat) emitted from the heaters,,, andtoward certain regions of the lower belt.

In the present embodiment, the second heating unitof the lower belt unitis disposed inside the lower beltand below the nip portion N to heat the lower beltfrom the inside. The second heating unitincludes a plurality of heating portionsand. In the present embodiment, the two heating portionsandare arranged side by side in the rotation direction of the lower belt.

The reflectorsandare disposed to cover the peripheries of the heaters,,, andexcept for the side facing the lower belt. That is, the reflectorsandare formed such that the heaters,,, andare open downward and both ends of the heaters,,, andin the width direction are covered. Thus, the reflectorsandefficiently radiate the radiant heat of the heaters,,, andtoward the lower portion of the lower belt.

That is, in the lower belt unit, the certain regions are regions of the inner peripheral surface of the lower beltoutside the nip portion N, and is a lower portion of the lower beltin the present embodiment. Specifically, the regions heated by the plurality of heating portionsandare regions of the inner peripheral surface (lower surface portion) of the lower beltbetween the guide rollerand the guide rollerin the rotation direction of the lower belt. That is, the certain regions of the lower belt unitare regions of a surface of the lower beltstretched in the substantially horizontal direction by the guide rollerand the guide roller. As described above, the lower belt unitis provided with the padat a position corresponding to the nip portion N, and cannot directly heat the nip portion N unlike the upper belt unit. Therefore, by arranging the plurality of heating portionsandto face the above-described region of the lower belt, the lower beltis efficiently heated in a direct manner.

The regions of the lower beltheated by the plurality of heating portionsandare on the downstream side in the rotation direction of the lower beltwith respect to the central position between the guide rollerand the tension rollerthat stretch the lower portion of the lower beltin the rotation direction of the lower belt. Therefore, the lower beltcan be heated at a position relatively close to the nip portion N by the plurality of heating portionsand, and heat can be efficiently transferred to the sheet S passing through the nip portion N. In addition, the heating portionsandperform temperature adjustment control such that the temperature of the lower beltis maintained at a predetermined temperature, by controlling the input power based on a value detected by a temperature sensorthat detects the surface temperature of the lower belt.

When the rotation detection sensorsanddetect the rotation of the belt has been stopped, the heating by the heating portions,,,, andis stopped. As a result, it is possible to suppress an occurrence of local heating caused by heating in a state where the upper beltand the lower beltare stopped.

Next, the heating portions,,,, andwill be described in detail with reference to.is an enlarged cross-sectional view illustrating the peripheries of the heating portions,,,, andof the fixing belt unit, andis a cross-sectional view illustrating the heatersandand the reflector. Since the heating portions,,,, andprovided in the upper belt unitand the lower belt unitbasically have a common configuration, the common configuration will be described by taking the heating portionas a representative.

The heating portionincludes two heatersandhaving different maximum powers. The ends of the heatersandin the width direction are supported by a support portion (not illustrated). The heatersandin the present embodiment are halogen heaters, and the heateris a heater to which a power higher than that of the heatercan be supplied. That is, the heatercorresponds to a first heater, and the heatercorresponds to a second heater having a power lower than that of the heater

The heatersandare covered with the reflector, and heat the upper beltimmediately below the heatersand. The reflectoris formed, for example, using a mirror-finished aluminum member or the like, and reflects light generated from the heatersandto concentrate the light on a certain region of the upper belt.

As illustrated in, the reflectorhas a shape having a part of a parabola. The reflectoris a parabola having a reflector apexas an apex. The parabolic shape formed in a direction from the reflector apextoward the upper beltextends to reflector parabola end points, and then extends toward the upper beltin a substantially vertical direction to form reflector straight portions. Note that the shape of the reflectormay be approximated by a polygonal shape made up of a plurality of line segments due to restrictions in manufacturing parts or the like. The reflector straight portionsare preferably arranged as short as possible (which may be 0), but are provided to secure a space for arranging a temperature sensorto be described below.

With respect to a focal point (reflector focal point)of the parabola guided by the reflector apexand the reflector parabola end points, the heatersandare disposed closer to the upper beltthan the reflector focal point, and are disposed with a difference in height in the up-down direction. Further, the heaterto which a high power can be supplied is disposed to be shifted downward from the heater

That is, the cross-sectional shape of the reflectorincludes the reflector apex, the reflector parabola end point, and the reflector straight portionextending from the reflector parabola end pointtoward the upper belt. With respect to the focal pointof the approximate parabola passing through the reflector apexand the reflector parabola end point, the two heatersandare disposed at positions closer to the upper beltthan the focal point, and the two heatersandare located at different distances from the upper belt.

The positions of the heatersandcan be defined as follows. Since the heatersandsatisfy the following requirements, the heaterwill be described as a representative below. First, a line drawn from the heatertoward the reflectorin a direction orthogonal to the perpendicular line drawn from the heaterto the upper beltand orthogonal to the width direction of the upper beltintersecting the rotation direction of the upper beltis defined as an incident light segment. A point at which the incident light segment λintersects the inner surface of the reflectoris defined as a first intersection P. A line drawn from the first intersection Psuch that an incident angle and a reflection angle are the same in relation to the incident light segment λis defined as a reflected light segment. A point at which the reflected light segmentintersects the upper beltis defined as a second intersection P. A point where a perpendicular line V drawn from the first intersection Pto the upper beltintersects the upper beltis defined as a third intersection P. In this case, the heateris disposed such that the second intersection Pis closer to the heaterthan to the third intersection Pin the rotation direction of the upper belt.